We wish to purify and characterize the products of the platelet release reaction and to study their function in thrombosis and cell growth. Using affinity chromatography we have purified human platelet factor 4 to apparent homogeneity and determined the complete amino acid sequence of this first 70 residue protein. We plan to modify and identify specific residues essential to the known heparin binding property of platelet factor 4. We will examine the relative binding of heparin to antithrombin 3 and to platelet factor 4 and to antithrombin 3 and platelet factor 4 complexed with the platelet factor 4 carrier proteoglycan, which will be purified also by affinity chromatography. Platelet factor 4 intrinsic to the platelet will be compared with platelet factor 4 extruded during the platelet release reaction to determine if platelet factor 4 is modified during its release. We will seek binding of platelet factor 4 to the platelet, using the purified factor alone and platelet factor 4 in association with the carrier proteoglycan. Platelet factor 4 and the proteoglycan molecule will be purified also from rabbit blood and injected into rabbits to determine the circulating half-life and metabolic fate of each. These determinations will be done also in animals on heparin treatment. Using an apparently monospecific antibody obtained in rabbits against purified platelet factor 4, we plan to develop a radioimmunoassay to platelet factor 4. We plan to purify and characterize the fibroblast growth factor release from platelets during coagulation. Once purified, the proliferative response of cells will be examined with respect to DNA synthesis, cell cycle, and cell density.